UT2004 runs better than UT2003.
Edit: Just played the pack. Wow. These maps are either bad or worse. One of the maps, Attrium, is the worst map I've
EVER seen, thus I included a screenshot. I've seen a lot of maps, but this one takes the cake. It doesn't even have weapons! Look at the skybox for f*ck's sake! Another one, Infinity or whatever, is square rooms attached by incorrectly-made warpzones. It's supposed to give you the look of it going on forever, but all it really does is give you a nice HOM at the end of the halls. None of these maps flow with any sort of real playability. The best maps (I use the term "best" loosely) are GhostTrain and SkyHaven, but they're both floating platform maps - something no one actually wants to play on.
My advice: Stay away from this pack. I give it a 2/10.